In the field of micro- and nanotechnologies, the trend is to reduce the size of the components and to increase their integration density. This trend must necessarily be followed by the interconnection technologies (conductive films and adhesives, flip-chips (1), etc.), for which the pitches are increasingly small.
A first example relates to the flip-chip which is a highly advantageous technique for hybridizing components, for example on read circuits (FIG. 1). Compared with other techniques such as wire-bonding, it serves to obtain a high interconnection efficiency and to make the components operate at high frequency. Moreover, this collective technique serves to obtain a self-alignment of the components (FIG. 2).
The present method for producing indium chips is illustrated in FIG. 3. The quantity of material required for the formation of the indium chip is deposited by lift off on a metal bump, and the board is then heated to a sufficient temperature to remelt the indium: the metal then assumes its chip shape.
This embodiment involves a delicate technological step, lift off, which requires the use of thick resins and a good control of their profile, and also a remelt step to obtain the actual indium chip. The chips have a typical diameter of about 10 μm, with a pitch of 15 μm, as shown in FIG. 1. With this technique, it becomes difficult to obtain smaller chips, with high densities.
For finer pitches and/or smaller chip sizes, other production methods, such as conventional photolithography, with plasma etching of the indium (with a carbon chemistry) or electrolytic growth, are used. However, these embodiments have not reached maturity today.
A second example relates to the field of anisotropic conductive films/adhesives. These adhesives contain particles which, crushed by thermocompression, cause a vertical conduction. In this field, it is also necessary to use increasingly thin films, with increasingly dense interconnections. At present, Anisotropic Conductive Films (ACF) which have the smallest conductive particles are products with 3 μm diameter particles.
The technical problem that the present invention proposes to solve is therefore to provide a method for manufacturing flip-chips having the desired structural characteristics, in particular having a smaller size, and a high density per unit area.
A further object advantageously pursued by the present invention is to offer a method which eliminates the photolithography steps used in the prior art.